NBC 5 Investigates is learning more about Derick Lamont Brown and his role as the national head the New Black Panthers' armed militia.
Police say Brown, 36, fatally shot his roommate Monday before shooting and critically wounding a neighbor along with a responding Dallas Fire-Rescue paramedic. Brown then killed himself.
On Tuesday, the FBI confirmed it was investigating Brown before Monday's shooting but will not say why there was an active investigation.
NBC 5 Investigates has learned Brown served as the national military commander for the New Black Panther Party, a group that's been on the radar for federal and local law enforcement.
Videos and photos on Facebook highlight Brown's role as a leader for the group, where he was also known as D.K. Egun Yomi or "Brotha DK."
In a 2014 video posted on YouTube, he's seen marching with a rifle at a protest over the death of a black man in East Texas.
"Mr. Brown is well known to state and local law enforcement," said Eric Jackson, special agent in charge of the FBI office in Dallas.
Jackson would not provide details on the FBI's investigation into Brown.
"Because of this being an open and active investigation we are not at liberty to discuss the nature of that investigation," said Jackson.
Brown was also a member of the Huey P. Newton Gun Club – a Dallas-based black nationalist group which conducts paramilitary training and advocates the open carry of firearms.
The national head of that club, Babu Omowale, described Brown as a tough guy who was in charge of training the militia portion of the organization.
Omowale said both groups are aware the FBI keeps tabs on them, but he does not believe Monday's shooting had anything to do with the Panthers or the gun club.
"As a group we didn't have any involvement in the incident. We would never give the go-ahead for such a malicious act," said Omowale.
Omowale said on behalf of the club he wanted to extend prayers to the family of the injured paramedic. While his group has had disagreements with law enforcement Omowale said they wish only the best to first responders who help people.
Last summer the gun club attracted attention from police after the deadly ambush on Dallas police officers downtown.
Members of the group carried rifles in the protest that preceded the attack, but the group denied the shooter, Micah Xavier Johnson, was a member even though they acknowledged knowing him from community events he attended.
It's unclear whether the FBI's ongoing investigating into Brown was part of any wider investigation of black separatists groups.
And it's still a mystery what caused Brown to shoot his roommate, a neighbor and a Dallas paramedic before killing himself.
"We all want to find out what was it that drove our brother to commit this crime," said Omowale.
The national spokesman for the New Black Panther Party, Quanell X, told NBC 5 Investigates his group has no comment on what happened in Dallas on Monday.